(739b) Autocatalytic Decompostion of Chiral Aspartic Acid On Cu(110) Surface

Gellman, A. J., Carnegie Mellon University

Surface explosion is a phenomenon in surface science wherein an autocatalytic increase in the reaction rate during heating results in its occurrence over a very narrow temperature range. We have previously demonstrated that this phenomenon can be successfully exploited to attain extremely high enantioselectivity in the case of tartaric acid decomposition over naturally chiral Cu(643)R&S surfaces. Prior work by others has focused majorly on developing models that describe this phenomenon, however, little efforts have been directed towards understanding the factors in the mechanism of surface explosion that contribute towards observed enantioselectivity. In this regard, tartaric acid as a probe molecule has several limitations, the most important being the fact that, isotopically labeled enantiomers of tartaric acid are not commercially available.

In our most recent study, we have successfully identified aspartic acid as a probe molecule for studying autocatalytic decomposition on Cu(110) surface. Also, we have identified the differences in the kinetics of formation of these products as manifested in the temperature programmed reaction spectroscopy experiment. Using isotopically labeled species, we are now in a position to map the appearance of the atoms in the products from their location on the decomposing parent molecule.

In due course, various isotopically labeled species will be used for further investigation of this reaction to develop our understanding of the surface explosion phenomenon. Preliminary experiments on chiral Cu surfaces indicate that the aspartic acid should also prove to be an ideal probe for investigating the origin of extremely high enantioselectivity as observed in the case of tartaric acid decomposition on Cu(643)R&S surfaces. The ultimate objective of the work is to apply the experimental and parameter estimation techniques developed during the course of study on Cu(110) surface, towards the study of chiral aspartic acid enantiomer decomposition on chiral Cu surfaces. The idea is to be able to identify the mechanism, develop models that best describe the mechanism and finally, to identify the steps in the mechanism that lead to enantioselectivity i.e. to figure out the rate constants that depend on the chirality of the surface.